filter caps and tone

[iknowjohnny]

Thanks, i'll give that a shot. It may at least show a wide variation between the 2 amps. But as to whether AC balance is a good thing or not, there was some discussion on this at 18watt recently where it was suggested that AC balance there was a hi-fi thing and not necassarily good for guitar amps due to the lessened even order harmonics it makes for. I suggested maybe it's because back in the day Leo didn't take that into account for obvious reasons and simply followed the RCA handbook, and that later amps followed him. It was said that may well be true and that AC balance is probably not a good thing. Then i looked at a lot of schematics for contemporary designs and noticed they indeed in many cases seem to have eliminated the mismatched plate resistors on the PI which i was told when matched creates DC balance but AC imbalance for more even order harmonics. I tried this by replacing the 82k on one side of the PI with a 100k and it did seem to sweeten the tone. i won't say it wasn't placebo effect, but it seemed that way. In any case i'd be interested to hear more thoughts on that theory. And i'll try what you said, tho i will have to see if theres something around here i can generate a signal with because i have no signal generator. I might have a old tiny yamaha keyboard around here with a sustaining organ sound. i'll have to look. Thanks.

[rockford]

while on this subject, heres a question... has anyone used RIFA caps, and how do they sound, bright, dark etc.

[skyboltone]

its equal AC measured from ground at the grids of the power tubes....
or as close to zero measured between the grids...... this is done with a signal
applied to the amp.......

DC balance is measured between the plates of the inverter tube with no signal......
theres some discussion of this on dumble forum..... to find the magic spot
but all textbook discussions of push-pull amps assume identical tubes on each
side of the inverter.....equal DC ..... and equal AC at the grids of the power tubes
this is not always reality..... but AC balance really improves performance

Let's talk about this for a minute Andy. Can you really measure this AC signal at the power tube grids with a DMM reliably? Won't this load the circuit and disturb the PI plate load impedence enough to kinda build false security? Wouldn't a decent VTVM be a better tool? Then, does crossover distortion disturb the phase angle enough to make zero not really zero at all? Do you use a DC balance pot at the PI plates to facilitate these tests?
And BTW these are questions, not challenges, I've really never approached tone this way. I'm more of a switch and listen kind of a guy but that sure gets tedious at times.

[Andy Le Blanc]

good points...... and in a dynamic circuit yes a VTVM would be a better choice
when measureing RMS between the grids.... but when the reading is taken from
ground or if the measurement is taken with the power tubes removed a DMM
should be adequate......

now .....crossover distortion is an occurance that happens as a result of the
bias conditions associated with power tubes when operating in push-pull.....
and not in the output of the phase inverter that is used to meet the
requirements of push-pull..... and has nothing to do
with the phase angle(s) of the signal(s) that result from the inverter stage...

but its also completely to the point...... the requirements for push-pull are two
signals of equal magnitude but 180 degrees out of phase..... and its how well
the inverter fullfills this task that is determinant of the subjective quality of
the circuit.....like screen grids....there are practical requirements and then
there are subjective qualities.....

with a long tailed chathode coupled inverter ala. fender its easy to install
a balance pot in the plate circuit...and there are a couple ways to do it.....
but with this inverter you cant with the one pot. balance DC and AC at the same time.....
so start with the AC balance to meet the push-pull requirements then go
thru various steps of imbalance between where the AC is balanced and
where the DC is balanced and listen subjectively or run a signal at various
gain levels and view the results thru any sort of spectrum analyser to get
an idea of how the ratios of even and odd orders of harmonic distortion
are affected and compare to what you like to hear......